. The Biological bulletin. Biology; Zoology; Marine biology. HETEROTYPICAL MITOSIS IN NEREIS LIMBATA. 61 The maturation process in the egg of Nereis does not begin until fertilization has taken place, and the earliest stages contained in my material show the nuclear membrane still unbroken, while outside of it two small asters have made their first appearance. Within the large nucleus fourteen chromosomes are found scat- tered around, most of them, however, lying relatively near to the nuclear membrane. The chromosomes appear in shapes, well known from other worms — Allolobophora (Foot and Str
. The Biological bulletin. Biology; Zoology; Marine biology. HETEROTYPICAL MITOSIS IN NEREIS LIMBATA. 61 The maturation process in the egg of Nereis does not begin until fertilization has taken place, and the earliest stages contained in my material show the nuclear membrane still unbroken, while outside of it two small asters have made their first appearance. Within the large nucleus fourteen chromosomes are found scat- tered around, most of them, however, lying relatively near to the nuclear membrane. The chromosomes appear in shapes, well known from other worms — Allolobophora (Foot and Strobell, 1905), Tomopleris (Schreiner, 1906a) and others — forming rings and crosses of dif- ferent kinds ; but they also very often appear in a more irregular shape. (See earl, proph. of 1st mat. div. ; p. 62.) A comparison of these different chromosome forms shows. b c d e f g Fig. 1, a-g. Schematic illustration of the development of chromosomes from the original tetrad. Explanation in the text. that they all are reducible to one and the same type — to a more or less elongated tetrad (Fig. 1, a) in which the four originally parallel elements maybe arranged in different ways (Fig. \,b-g). In most cases the four elements are combined in pairs, so as to give the appearance of two longitudinally split ribbons, connected at one (Fig. 1, b ; chrom. 1, p. 62), or at both ends ; in the latter case the chromosomes form more or less typical rings (Fig. 1, c ; chrom. 4-6, p. 62). In other tetrads we find the four elements connected at one end, but diverging from this point in different directions (Fig. 1, d). Such an arrangement gives rise to cross-shaped chromo-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lillie, Frank Rattray, 1870-1947; Moore, Carl Richard, 1892-; Redfield, Alfred Clarence, 1890-; Marine
Size: 2494px × 1002px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectb, booksubjectzoology
